ERBB2 and neoplasm: (i) HER2 immunohistochemistry 3+ staining of less than 100% of sampled tumor cells shows weaker association with pCR and higher RCB scores following HER2-directed neoadjuvant chemotherapy compared to tumors with virtually 100% of cells exhibiting 3+ staining, despite all currently categorized as HER2 positive by CAP/ASCO.